We have a Moto SB5101 (DOCSIS 2.0), which the support page:
»ww2.cox.com/residential/support/ ··· 00000000
says is only compatible with "Starter and Essential packages".
However, we have been using it fairly reliably on the Preferred package (VOIPo SIP adapter failures finally isolated).
Until, my brother (accountholder) spoke with billing and was offered and accepted a 6-month free upgrade to Premier (DOCSIS 3.0 required).
The billing rep apparently wasn't made aware of the hardware incompatibility, which hit us hard, with wide swings in bandwidth, packet loss, latency, the whole shebang. Just requested from Juan U. at internet support chat that we be downgraded back to Preferred, but it's not showing the change yet or any improvement in service.